Blender cycles won't render halo particles
To render Halos in Cycles you need two objects: an emitter object with a particle system, and a second object that acts as a domain. The domain object should enclose the emitter object plus the area where the particles will be.



On the domain object you can use the Texture->Point Density node to control an emission shader that will be used as volume for the domain:

 

Select as Object the emitter object and its particle system, plug the density to the strength of the emission shader and lastly plug the emission as the volume for the domain's material. 





Example file:



NOTE: Currently (version 2.76) this method works only on CPU rendering, no GPU yet...